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Over-the-counter diet pills and tea that were banned from the market nearly two years ago because of contamination with dangerous chemicals remain widely available in Greater Boston and popular among Brazilian women seeking to shed pounds, according to a new study by Harvard Medical School researchers.

The pills and tea, known as Pai You Guo, are tainted with two pharmaceutical substances prohibited by US regulators because of increased risk of heart attacks, strokes, and cancer among users of the products.

But news of that prohibition has failed to reach consumers, the Harvard team discovered: None of the Brazilian women surveyed by the researchers had heard about the ban.

“They are just struggling to lose weight and wanting to try anything that might work,’’ said the study’s lead author, Dr. Pieter Cohen, an internist at Cambridge Health Alliance and an assistant professor at Harvard.

With a willowy woman adorning its golden package, Pai You Guo, made in China, is marketed as a natural way to lose weight and is sold in Chinese apothecaries alongside bins of ginseng, slabs of shark’s fin, and other traditional Chinese herbs and spices. The Globe found the product last week in two shops in Chinatown.

“People . . . have the understanding that it only contains natural herbal ingredients, so it must be safe,’’ Cohen said. “But that couldn’t be further from the truth.’’

The US Food and Drug Administration announced the recall in 2009 because the product was found to contain two dangerous substances, sibutramine and phenolphthalein.

Cohen’s study, published today in the Journal of General Internal Medicine, surveyed 565 Brazilian women from last October to January in a health clinic and several churches in Greater Boston and found that 23 percent said they had taken Pai You Guo. Most of the women who had used the supplement said they purchased it since the recall.

The researchers targeted Brazilian women because alternative diet products are popular in their community.

Nearly 30 percent of women who used the product said they bought it at local stores, and 9 percent bought it over the Internet. Two-thirds said they purchased it from an acquaintance.

The majority of users reported at least one adverse side effect, most typically dry mouth, anxiety, and insomnia. But some reported more serious health problems, including heart palpitations, depression, fainting, nausea, and vomiting.

Lucimara Rodrigues, a 27-year-old Allston resident, said in an interview with the Globe that she had not heard about the ban when she started taking the pills earlier this year for several weeks. They made her sick.

“I had vomiting and diarrhea for three days,’’ the Brazilian immigrant said through a translator. A friend had recommended the supplements because they helped her lose a lot of weight. Rodrigues did not lose a pound.

Over the past several years, the FDA has issued consumer alerts regarding nearly 300 tainted products marketed as dietary supplements and received numerous injury reports associated with the products, marketed for weight loss, body building, or sexual enhancement.

Still, the supplement industry is booming, with nearly $23 billion in sales last year for weight-loss and sports nutrition products, according to the Nutrition Business Journal.

Unlike prescription medications, which are scrutinized by the FDA for safety and effectiveness, dietary supplements are largely exempt from regulatory oversight because of a 1994 law.

But officials are authorized to seize supplements if they are found to be tainted with pharmaceutical ingredients, as are Pai You Guo, Superslim, and dozens of other weight-loss products.

“The FDA has been really remiss in this whole area,’’ said Dr. Sidney Wolfe, director of health research at Public Citizen, a consumer watchdog group.

Wolfe said the agency has been slow to go after companies, even after discovering tainted supplements.

“One can imagine this won’t get better,’’ Wolfe said. “It will get worse, because the former head of the dietary supplement trade association is now head of the FDA’s dietary supplement division.’’

Daniel Fabricant - a vice president of the Natural Products Association, the nation’s largest dietary supplement trade group - became chief regulator of the industry earlier this year.

Siobhan DeLancey, an FDA spokeswoman, said the agency is aggressively monitoring dietary supplements, and she branded as absurd Wolfe’s assertion that the agency would slack off because of Fabricant’s past industry ties.

“The argument is abjectly ridiculous,’’ DeLancey said. “These products are a priority for the agency.’’

While Fabricant oversees dietary supplements, she said, he would not be in charge of those found to be adulterated. Those products, she said, are regulated by another FDA division.

DeLancey said tainted weight-loss products are typically made in foreign countries and sold by smaller distributors, making it difficult to track down the companies manufacturing the substances, which, she said, are flooding into the United States.

DeLancey said she was not surprised by the Harvard researchers’ findings.

“We know it’s really hard to reach consumers [about product recalls and health alerts], and we are still battling to find a way to reach as many people as possible,’’ DeLancey said.

Glauciane Silva, a 30-year-old Brazilian immigrant and a Woburn mother of two, wanted to buy Pai You Guo to help shed 15 pounds she has been unable to lose since childbirth. But her husband would not allow it because, Silva told a reporter, she is still battling significant health problems from another tainted diet product.

Two years ago, Silva took Superslim and suffered painful gallstones. “I was having shortness of breath and all I wanted to do was lay down, and I felt a lot of pain in my stomach,’’ Silva said through a translator.

“Now that I stopped taking the medication, I am feeling fine,’’ she said, “although I am now overweight.’’

Globe correspondent Jialu Chen contributed to this report. Kay Lazar can be reached at klazar@globe.com.